This invention relates to an apparatus for controlling an elevator which is driven by an induction motor.
FIG. 5 is an arrangement diagram which shows a prior-art control apparatus for an A.C. elevator disclosed in the official gazette of Japanese Patent Application Laid-open No. 22271/1983 by way of example.
Referring to the figure, numeral 1 designates a converter which is connected to the phases R, S and T of a three.-phase A.C. power source and in which a three-phase full-wave rectifier circuit is constructed of thyristors 1a-1f. Connected across the D.C. side of the converter 1 is a smoothing capacitor 2 which smooths the D.C. output of the converter 1. Numeral 3 designates an inverter which is connected across both the terminals of the smoothing capacitor 2 and which is constructed of, e.g., thyristors. This inverter 3 inverts direct current into alternating current, the voltage and frequency of which are made variable. A three-phase induction motor 4 is connected to the A.C. side of the inverter 3, a brake wheel 5 is coupled to the motor 4, a brake shoe 6 is disposed in opposition to the outer periphery of the brake wheel 5 and applies a braking force to the brake wheel 5 owing to the force of a spring (not shown), and a brake coil 7 operates when energized, to separate the brake shoe 6 from the brake wheel 5 against the force of the spring. A driving sheave 8 for a hoist is driven by the motor 4, a main rope 9 is wound round the sheave 8, and a cage 10 and a counterweight 11 are coupled to the main rope 9. The contacts 12a-12c of an operating electromagnetic contactor, which are respectively inserted between the power source phases R, S and T and the converter 1, are closed when running the cage 10 and are opened when stopping it. The contacts 13a-13c of an operating electromagnetic contactor, which are inserted between the inverter 3 and the motor 4, are closed after the closure of the contacts 12a-12c and are opened after the opening of them. Numeral 14 indicates a rectifier circuit which is connected between the power source R, S, T and the smoothing capacitor 2 and in which a three-phase full-wave rectifier circuit is constructed of diodes 14a-14f. A resistor 15 is inserted on the D.C. side of the rectifier circuit 14.
With the prior-art control apparatus for the A.C. elevator constructed as described above, while the cage 10 is at a stop, the brake shoe 6 depresses the brake wheel 5 owing to the force of the spring. In addition, the smoothing capacitor 2 is normally charged through the rectifier circuit 14 as well as the resistor 15.
When a start command has been given to the cage 10, the contacts 12a-12c of the electromagnetic contactor are closed, and the converter 1 produces a D.C. output. Since, however, the smoothing capacitor 2 is charged beforehand, the rapid charging of the smoothing capacitor 2 by a low-impedance direct current attributed to the converter 1 can be avoided. Thus, the D.C. output of the converter 1 is supplied to the inverter 3, and the control elements (not shown) of the respective arms of the inverter 3 are successively turned `on` according to a running direction and generate A.C. outputs of variable voltage and variable frequency in a phase sequence corresponding to the running direction. The contacts 13a-13c of the electromagnetic contactor are closed, and the above outputs are supplied to the motor 4. At the same time, the brake coil 7 is energized, so that the brake shoe 6 comes away from the brake wheel 5. Thus, the motor 4 starts in a direction determined by the phase sequence of the inputs, and the cage 10 begins to run.
In the prior-art control apparatus for the A.C. elevator as described above, the smoothing capacitor 2 is normally charged through the rectifier circuit 14 in order to prevent the rapid charging. This leads to the problem that the circuit arrangement becomes complicated.